1. Field of the Invention
The present invention relates, in general, to a display apparatus and, more particularly, to a pixel unit scanning-based display apparatus, in which diffracted beams having a plurality of diffraction orders, formed from a single beam through diffraction, are used to display images in such a manner that each pixel can form a plurality of dots on a screen by vibrating the diffracted light generated in pixels.
2. Description of the Related Art
Nowadays, printer technology is on the expressway towards high speed, miniaturization, high resolution, and low cost. A typical laser printer employs a laser scanning scheme of scanning laser beams using a laser diode and an f-θ lens.
In order to realize a high speed printer, an image head scheme using a multibeam beamformer has been adopted. In such a scheme, high speed and high quality can be realized, but a high cost is also incurred because it requires a plurality of light sources.
FIG. 1 illustrates an example in which a conventional laser scanning scheme using a single light source and an f-θ lens is used. As shown in FIG. 1, an example of the operation of the laser scanning scheme is described below. If a light beam is generated by a laser diode (LD) 10 in response to a video signal and passes through a collimator lens 11, the light beam is collimated into parallel light and is further converged on a polygon mirror 13 by a cylinder lens 12. While passing through the cylinder lens 12, the parallel light beams are converted into linear light beams parallel to a scanning direction.
Rotating at a constant speed, the polygon mirror 13 driven by a motor deflects the linear light beams incident thereon and scans them in the direction of an f-θ lens 15.
Thereafter, the linear light, scanned at a constant angular velocity by the polygon mirror 13, is deflected by the f-θ lens 15. Simultaneously, aberrations in the deflected linear light are corrected. The linear light beams with corrected aberration are reflected by a bend-back mirror 16 and scanned over a photosensitive drum 17 at a constant velocity due to the constant rotational speed of the polygon mirror 13.
In the laser scanning scheme, it is difficult to attain a high printing speed due to problems with a low switching speed of the laser diode 10 and a low scanning speed of the polygon mirror 13.
For example, an improvement in the scanning speed of the light beam in the laser scanning scheme requires the polygon mirror to rotate at a higher speed, thus requiring a high-speed driving motor. However, a higher speed motor may increase the production cost, and the motor rotating at high speed produces heat, vibration and noise, thus degrading the operational reliability of the apparatus provided therewith.
As another approach to improving the scanning speed of an optical scanning unit, an image head printing scheme, in which a multi-beam beamformer is utilized, has been suggested.
FIG. 2 shows an image head used in a conventional laser scanning scheme. As shown in this figure, an image head 20 has an LED array 21 composed of a sufficient number of LEDs 22 to cover a scanning width of a paper to be printed. In contrast to the laser scanning scheme, this image head printing scheme uses neither a polygon mirror nor an f-θ lens and forms a multibeam which allows all of the content of a line to be printed at the same time, thereby significantly enhancing the printing speed.
However, the image head printing scheme suffers from the disadvantage of having increased production cost because there is a large number of LEDs 22 in the LED array 21 and uniform images are not obtained because of low optical uniformity among LEDs in the array.